Cyclic Plasma Etching With Tungsten Passivation for ARDE Control
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Solution Overview
Problem
Conventional plasma etching methods face issues with polymer accumulation leading to reduced etch rates, aspect ratio dependent etch-rate (ARDE), and feature distortions due to polymer buildup on mask sidewalls, which conventional gas tuning methods fail to effectively address without compromising etch rate or mask selectivity.
Innovation Solution
A cyclical etching process incorporating a first etch step with a carbon-containing precursor gas to form a passivation layer and a second etch step with a tungsten-containing precursor gas to remove polymer accumulation and passivate sidewalls, using tungsten fluoride (WF6) to maintain sidewall passivation and control polymer buildup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional gas tuning methods are used to control polymer buildup, then polymer accumulation is reduced, but etch rate and mask selectivity are compromised
Solution Approach 1:
The patent implements a cyclical etching process that alternates between a fluorocarbon-based etch step (which generates polymer passivation) and a tungsten-based etch step (which removes polymer accumulation). This periodic switching allows the system to benefit from polymer passivation during etching while periodically clearing excess polymer, thereby maintaining high etch rates without compromising mask selectivity
Solution Approach 2:
The patent changes the chemical composition parameters of the etching plasma by switching between fluorocarbon-containing gases (CF4, C4F8, C4F6) and tungsten-containing gases (WF6, WCl6). This parameter change enables dynamic control of polymer formation and removal, allowing optimization of both etch rate and polymer management that cannot be achieved with single-gas chemistry
2Shape
If polymer buildup is allowed to occur for sidewall passivation, then etch anisotropy is improved, but aperture shrinkage and feature distortions occur
Solution Approach 1:
The patent extracts the harmful polymer accumulation from the system by introducing a tungsten-based etch step that selectively removes polymer from the aperture region while leaving the sidewall passivation intact. This separation allows the system to maintain vertical sidewalls without suffering from aperture shrinkage
Solution Approach 2:
The cyclical process creates different local conditions: during fluorocarbon etching, polymer accumulates locally on sidewalls providing passivation; during tungsten etching, polymer is removed locally from aperture regions. This spatial differentiation of polymer management resolves the contradiction between needing polymer for shape control and removing it to maintain aperture area
3Area of stationary object
If polymer accumulation is reduced to maintain aperture, then etch rate improves, but sidewall passivation is insufficient leading to feature distortions
Solution Approach 1:
The periodic alternation between fluorocarbon and tungsten etching steps ensures that sidewall passivation is continuously replenished during fluorocarbon steps while aperture regions are periodically cleared of excess polymer during tungsten steps, maintaining both aperture area and feature shape
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The cyclical etching process effectively controls polymer accumulation, reduces feature distortions, improves etch rate consistency, and enhances mask selectivity by using tungsten passivation to manage polymer buildup, thereby minimizing ARDE and feature defects.
Implementation Method 1
forming a first passivation layer including a polymer material over sidewalls of the openings
Implementation Method 2
performing a second etch step to remove a portion of the first passivation layer, performing the second etch step including generating a second plasma from a tungsten containing precursor gas
Data Source
AI summary
A method of plasma etching a substrate includes cyclically performing a first etch step to etch a target material, the substrate including a patterned mask disposed over the target material and having openings in the patterned mask, performing the first etch step including generating a first plasma from a carbon containing precursor gas and exposing the substrate to the first plasma to form a first passivation layer and etch the target material, the first passivation layer including a polymer material over sidewalls of the openings. And the method further includes cyclically performing a second etch step to remove a portion of the first passivation layer, performing the second etch step including generating a second plasma from a tungsten containing precursor gas and exposing the substrate to the second plasma.